Teacher's Answer Key

1. NASA is concerned about the amount of radiation that your crew will be exposed to while on your trip. The table below shows the minimum and maximum dosages ( in rads/day) that were received for different Space Shuttle flights, and at different altitudes given in Nautical Miles (NM). Find the combined average dosage.

STS-38 125 NM0.003 0.004
STS-51G 200 NM 0.015 0.020
STS-37 245 NM 0.040 0.070
STS-31 330 NM 0.140 0.2201

Average combined dosage in rads/day = 0.064

2. Suppose that NASA decides to send the expedition at a time near solar maximum. By the time you return, the conditions in space will be near those at solar minimum during the solar cycle which occurs about 5.5 years after solar maximum. During solar maximum, the sun is very active and effectively shields the inner solar system from most of the galactic cosmic rays (G4CRs) which contain very high energy particles. During solar minimum, the Sun is relatively inactive and allows GCRs to reach the inner solar system in greater numbers. The integrated dose of GCRs is about 2.5 times higher at solar minimum than at solar maximum. Using the data in the table above during conditions of solar maximum, calculate the average dosage in rads/day during solar minimum.
Average dosage in rads/day during solar minimum = 0.064x2.5 = 0.16

3. The next step in the process- is, to determine the number of rads/day for the crew. Also, you will need to calculate the total exposure over the entire 4.3 year trip. Total exposure is measured in units of rems. Your trip begins during solar maximum and ends during solar minimum. On the graph below, calculate the number of rems/day for each time period. Assume that while on Mars that you are adequately shielded with a natural background dose of 15 rem per year ( or 0.04 rads/day). To calculate rems: Rads per day multiplied by the number of days of exposure number of rems of total radiation dosage.

Number of rems on trip to Mars = 0.064x240days = 15.4 rems
Number of rems on Mars= 0.04 x (1335-240) = 43.8 rems
Number of rems on trip to Earth= 0.16 x 240 days = 38.4 rems